1. Field of the Invention
The present invention relates to a multi-function sensor using a semiconductor laser, and more particularly to a multi-function sensor using a semiconductor laser capable of sensing a value of a measurement object such as temperature, humidity, pressure or vibration on the basis of a variation in distance between the measurement object medium adapted to respond to a variation in the measurement object and a focus of laser beams projected onto the measurement object medium.
2. Description of the Prior Art
Generally, a sensor for measuring a temperature of an object includes a thermocouple adapted to generate a thermal electromotive force corresponding to the temperature of the object measured at a point where the measurement is carried out. The sensor detects a voltage corresponding to the thermal electromotive force and thereby senses the temperature of the object.
Referring to FIG. 1, there is illustrated a conventional temperature sensor utilizing a thermocouple. As shown in FIG. 1, the temperature sensor includes a thermocouple T for generating a thermal electromotive force corresponding to a temperature of an object detected at a point p where the measurement is carried out, a linearizer 1 for linearizing the thermal electromotive force output from a connection terminal board C of the thermocouple T, and a cold junction compensation circuit 2.
In the conventional temperature sensor, there is a temperature difference between the measurement point p and the connection terminal board C due to a low thermal electromotive force of about several ten microamperes per centigrade generated by the thermocouple and a distance between the measurement point p and the connection terminal board C. Furthermore, the thermocouple itself serves as a noise source. For these reasons, such a temperature sensor using the thermocouple is unsuitable as a device for sensing the object temperature to a high accuracy.
In order to provide a high accuracy, the temperature sensor requires an addition of expensive elements. In this case, the construction of the temperature sensor becomes more complex.
In cases of sensors for measuring humidity, vibration and pressure, such an addition of expensive elements is also required to obtain a high accuracy. As a result, such sensors inevitably entail a high cost and a complex construction. Furthermore, different control circuits and measuring circuits may be required for different objects to be measured, respectively.